An integrated friction launch clutch may be used instead of a torque converter as a coupling device in an automatic transmission during the vehicle launch process. A launch clutch usually comprises a pack of steel disks splined to a housing and friction plates splined to a hub, arranged alternately to provide disk-plate contact interfaces. The friction plates are comprised of a thin plate with friction material, segmented or un-segmented, attached on at least one side of the friction plate. A piston applies the clutch during vehicle launch. A launch clutch is slipped for a longer time than a shifting clutch. Thus, the heat generated in a launch clutch is higher than in a shifting clutch and efficient cooling is required to maintain acceptable steel disk and cooling fluid temperatures.
Grooves may be formed in the friction material so that cooling fluid, which is often oil, can flow through the grooves either from the friction plate outer peripheral edge to the friction plate inner peripheral edge, or from the friction plate inner peripheral edge to the friction plate outer peripheral edge. Heat generated in the steel disks is dissipated by conduction to the cooling fluid as the cooling fluid passes through the grooves and along the disk outer peripheral edge and disk inner peripheral edge. Insufficient cooling can result in undesirably high temperatures in the steel disk and in the cooling fluid, which may cause damage to the steel and friction material. It may also cause a break down of the base stock and additives in the cooling fluid. Improper cooling in the steel disk can cause localized hot areas or “hot spots,” which may result in distortion and damage to the steel disk and the friction material. Damage at the disk-friction material interface can adversely affect durability or function. The types of damage affecting durability include “burned” friction material, distorted steel plates, oxidized oil, and additive depletion in oil. The types of damage affecting functionality include changes in friction characteristics near the hot area that can lead to shudder and rapid reduction in torque capacity. A hot area can cause damage to the steel disk, the friction material, and the cooling fluid even if the average temperature of the material is within acceptable limits.